This section provides background information related to the present disclosure which is not necessarily prior art.
Activation of innate immunity is critical for vaccine development and immunotherapy, through triggering antigen specific immune responses. Natural Killer T cells (“NKT cells”) are a unique type of innate immune cells and a unique subset of lymphocytes that have markers and functions of T cells and NK cells. NKT cells can be activated within 2 hours of antigen (alpha-galactosylceramide) stimulation, and produce large amount of Th1 and Th2 cytokines. In addition to secreting cytokines, NKT cells play an extremely important role in initiating the cell-to-cell contact and crosstalk between several types of immune cells, including dendritic macrophages, CD4 T cells and CD8 T contrast to conventional T cells which recognize peptide antigens, invariant NKT cells recognize lipid antigens presented by the non-polymorphic MHC-like molecule CD1d.
Alpha-Galactosylceramide (KRN7000)
Alpha-galactosylceramide (αGalCer, also named as KRN7000), a potent immunotherapeutic, is a marine-sponge derived glycosphingolipid, such as the embodiment shown in U.S. Pat. No. 5,780,441. It is a super-agonist antigen for NKT cells and capable of limiting melanoma metastasis and inhibiting the replication of hepatitis B virus in mouse models through a Th1 cytokine (IFN-γ) mediated mechanism. In several clinical trials involving cancer patients and hepatitis C patients, alpha-galactosylceramide has been demonstrated to induce strong Th1 cytokine response.
Soluble Alpha-Galactosylceramide Induces Anergy NKT Cells
A major problem for alpha-galactosylceramide is it causes NKT cells non-responsiveness (anergy) after one dose of treatment, because alpha-galactosylceramide can be presented by CD1d expressing B cells in the peripheral blood as shown in FIG. 1A, thus stimulates the NKT cells without proper co-stimulatory molecules.
To overcome the anergy induced by soluble alpha-galactosylceramide, Dhodapkar and Steinmann have developed a cell therapy approach as shown in FIG. 1B, by intravenously injecting alpha-galactosylceramide pulsed, ex vivo generated dendritic cells from patients' peripheral blood mononuclear cells. The cell therapy method avoided the NKT anergy mechanism, and showed potent efficacy in cancer patients in eliciting tumor antigen-specific CD8 responses. However, cell therapy is expensive, and impracticable for virus infected patients since their tissues are excluded from GM′ processing. Hence, new methods are needed to stimulate NKT cells in vivo repeatedly and effectively.
Expansion, Contraction, and Memory Phase of NKT Cells after Drug Stimulation
As demonstrated in FIG. 2, the stimulation of NKT cells by a continuous release of alpha-galactosylceramide includes the expansion, contraction, and memory phases. In the expansion phase, the NKT cells produce anti-tumor and anti-viral cytokines. In contraction phase and memory phase, most NKT cells die, while 5 to 10% of “memory” NKT cells begin to “rest” and re-program themselves for the next stimulation. Thus a continuous release of alpha-galactosylceramide can not cause effective stimulation of NKT cells, instead, continuous release of alpha-galactosylceramide has been shown to cause the non-responsiveness (anergy) of NKT cells. Therefore, new methods are needed to cause rapid release of alpha-galactosylceramide upon being phagocytosed by dendritic cells and macrophages, but not consistent release of alpha-galactosylceramide to the serum.